Air pollution abatement system



Aug. 7, 1962 J. B. GREGORY ETAL AIR POLLUTION ABATEMENT SYSTEM Filed June 50, 1959 2 Sheets-Sheet 1 A? CLEd/VEI? JAMES B. GREGORY #0144420 12 EMEQS'aA/ CV/APAES C. M0045 i AMMw X 1 4M nite tates Patent 3,048,157 AIR POLLUTION ABATEMENT SYSTEM James B. Gregory, Charles C. Moore, and Howard D.

Emerson, Fullerton, Calif, assignors to Union Oil Company of California, Los Angeles, Calif, a corporation of California Filed June 30, 1959, Ser. No. 823,914 25 Claims. (Cl. 123136) This invention relates to the abatement of air pollution, and in particular concerns certain new and useful improvements in fuel systems for internal combustion engines, such as those employed for the propulsion of motor vehicles.

The operation of motor vehicles contributes markedly to the air pollution problem in large cities by the release of hydrocarbons to the atmosphere, either as unburned fuel via the exhaust system, or as evaporated fuel via the fuel supply system. A great deal of evaporated fuel originates from the motor vehicle engine carburetor, both during periods of-operation and non-operation. One of the major sources of these carburetor evaporation losses is from the carburetor float bowl, which is a vented reservoir of volatile fuel constantly exposed to heat from both the atmosphere and the engine. These evaporative losses are essentially a function of fuel volatility, float bowl temperature, and carburetor design.

Fuel vapors from the conventional float bowl can escape to the atmosphere along two principal routes: (1) directly to the atmosphere through external vents in the float bowl, and (2) through so-called internal vents or balancing tubes into the body of the carburetor. When the engine is running, hydrocarbon vapors escaping through the internal vents are drawn into the combustion chamber with incoming air and subsequently combusted. However, any vapors that escape through the external vents during this operational period 'will contaminate the atmosphere. When the engine is turned off, hydrocarbon vapors escape through both the internal and external vents to the atmosphere. However, since carburetors perform at widely varying temperatures with volatile fuels, some form of venting must be used to keep the float bowl at essentially the same pressure as the other communicating carburetor chambers when the engine is running.

One major cause of carburetor evaporation loss, only casually considered by previous investigators, is the socalled carburetor hot soak which begins immediately after the engine is turned olf. Heat stored by the engine while running is transmitted to the carburetor float bowl, which, depending on design, normally contains from around 80 to 200 ml. of volatile hydrocarbon fuel. As the trapped fuel in the float bowl is heated, evaporation occurs through the aforementioned carburetor vents.

Generally, there is a float bowl temperature rise of from about 40 to 60 F. from the bowl temperature at the time the-engine is shut off to the peak temperature reached (usually in about 20to 4O minutes)'during the hot soak period. It can be generallystated that atmospheric temperatures have little effect upon the hot soak temperature of the carburetor bowl, the bowl temperature seems to be controlled primarily by engine coolant temperature. Carburetor design has virtually no effect on hot soak losses, except in the matter offloat bowl fuel capacity. It has been found that normal losses to the atmosphere from the carburetor float bowl during the hot soak period range from to 30 percent of the fuel remaining in the float bowl at the time the engine is stopped.

It is accordingly an object of this invention to provide an improved method and apparatus for the abatement of atmospheric pollution resulting from the operation of internal combustion engines.

Another object is to provide an improved method and apparatus for effecting a substantial reduction in the ICC 2. gross fuel consumption of automobiles, thus resulting in more efiicient and economic operation.

A further object is to substantially reduce the evaporative fuel losses from the fuel supply system of internal combustion engines.

Other and related objects will be apparent from the following detailed description of the invention, and various advantages not specifically referred to herein will be apparent to those skilled in the art on employment of the invention in practice.

We have now found that the foregoing objects and their attendant advantages can be realized in a conventional internal combustion engine, such as is used in the propulsion of motor vehicles, by providing the float bowl of a conventional carburetor with a fuel drain line which returns the fuel remaining in the carburetor float bowl to the storage tank as soon as the engine is stopped. This removes the highly volatile hydrocarbons from the high temperature environment of the carburetor float bowl before any significant losses from hot soak can occur, thus eliminating a major source of air pollution.

The invention will be more readily understood by reference to the accompanying drawings which form a part of this application. FIGURE 1 is a schematic diagram of one of the simplest embodiments of this invention. FIGURE 2 is a schematic diagram of the apparatus of this invention in one of its preferred embodiments. FIG- URE 3 is a modification of the apparatus of FIGURE 1 wherein the fuel storage tank vent is connected to the vapor space of the carburetor fuel reservoir chamber. It is to be understood that although the float bowl draining method and apparatus of this invention is broadly applicable to any internal combustion engine using a volatile fuel and a fuel induction system, it is particularly useful for gasoline-burning engines, such as those used in automobiles, trucks, buses and the like.

Referring now more particularly to FIGURE 1, the

apparatus there shown consists essentially of the fuel supply system for an internal combustion engine. The fuel supply enters fuel tank ltl via inlet conduit 36. When fuel tank It has an adequate supply of volatile fuel, tank cap 38 seals inlet conduit 36. Tank vent 4Q. communicates with the atmosphere and, as is conventional with fuel storage tanks on motor vehicles, maintains fuel tank 10 at atmospheric pressure. Fuel is supplied to carburet or float bowl via line 12, fuel pump 14, and line 16. Fuel pump 14 can be any of the conventional pumps used in the fuel supply systems of internal combustion engines such as a vacuum-operated fuel pump, an electric fuel pump, a mechanical pump, or the like. The fuel enters carburetor float bowl 18 at a rate controlled by the characteristics of the fuel pump 14 and float valve 28 which, as it rises, restricts the outlet of line 16 into carburetor float bowl 18, thus acting as a liquid level control device to maintain a substantially constant level of fuel within carburetor float bowl 18.

- The foregoing constitute conventional elements found in nearly all carburetor fuel supply systems. According to our invention, a novel'fuel return system is provided in the form of a return line 30, opening from the bottom of bowl 18, and communicating in fuel delivery relationship with fuel tank 10 via drain valve 32 and line 34'. Valve 32 can be located at any intermediate horizontal level between the inlet to line 30 and the outlet of line 84, but for convenience of access is preferably located immediately below the carburetor body 20. Return lines 30 and 34 can be constructed of A: or inch I.D. tubing, such as is used for conventional fuel delivery lines. However, as will be more fully explained below, a suitable restriction to flow is incorporated into the fuel return system so that fuel from bowl 18 will not be returned to tank 10 at a faster rate than the supply system can deliver fuel to bowl 18.

s a i a i Onemethodof operating the apparatus as shown in FIGURE lis to have drain valve 312 in a blocked open position. There is then a constantly open drain -;line from float bowl 1% to fuel tank both when the engine is operating and when the engine is stopped. With'drain terial canbe' usedi such as. glasswool, .asbestos and the valve 32 blocked open and the enginerunning, fuel is continuously pumped from fuel tank 10 via fuel pump 14- to float bowl 18'. Simultaneously, fuel is constantly flowing from float bowl 13 to fuel tank 16 via line 30, blocked open drain valve 32', and line 34'. Thus, there is a constantly circulating flow of fuel from fuel tank lid to carburetor float bowl 18 andback to fuel tank 10, with an adequate reservoir level in carburetor float bowl 18 being like. i 1

Referring now more particularly toFIGURE 3 the apparatus here shown is a fragmentary view of the fuel.

supply system of FIGURE 1 with a modified fuel tank venting apparatus therein. The apparatus of FIGURE f 3 is identical in every respect to FIGURE 1 except for the direct connecting of tank vent d2 of fuel tank into maintained by float valve 218. The drainage capacity of I the fuel return system comprising line 36', valve 32, and line 34 is such that the flow through this return system is small compared to the total capacityof the fuel sup-. 7

ply system. Typically, the rate of gravity flow through the return system is about to /2' of the flow capacity supply in carburetor float bowl 18 during all conditions of" engine operation. A restriction such as an orifice, or the partial closing of drain it valve 32, can occasionally. be needed to prevent reverse surge in the drain line from the fuel tank during downhill drivingor rapid stops, resulting in overfilling of carburetor'bowl 18.

When the engine is stopped, fuel pump 14'no longer delivers fuel, as it is controlled by the engine operation. Carburetor float bowl 18 is then quickly emptiedof fuel via line 30, drain valve 3 2, and line 34; Thus, with the above-described mode of operation there is little fuel loss through external vent 22 to the atmosphere, since the highly volatile fuel has been removed from the carburetor float bowl within a few seconds to 3 or 4 minutes after the engine is stopped. When operation of the car 'is resumer fuel pump 14 quickly introduces fuel as herein before describedto carburetor float bowl 18 thus restoring the fuel therein to an adequate level for engine operation.

Line 34 can enter fuel tank 10 either in the vapor space at the top of the fuel tank or, in the preferred embodiment as shown in FIGURE 1, the drained fuel from carburetor-float bowl 18 can return to the bottom of fuel tank 10. Since this drainage fuel is usually warmer than the fuel in the fuel tank because of passing through the carburetor andthe engine compartment, the'preferred embodiment reduces evaporative fuel flashing by intro-- ducing said drainage fuelinto the bottom of the cool body offuel in tank 10. i

Further modifications of the apparatus. which have been highly successful in reducing evaporation loss, particularly during engine operation, involve the closing of external vent 22 by means of a plug or some other appropriate vapor-tight closure. A large variety of conventional carburetors have been operated with plugged ex-' ternal vents for extended periods of time in combination with the method and apparatus of our invention with a high degree of success. Evaporation losses from the fuel system were materially reduced, with a resultant reduction in atmospheric pollution and in gross fuel consumption. It has been found that as a further means of reducing evaporative losses of volatile fuels, fuel tank 10" should be insulated to reduce the acquisition of heat, thus lowering the temperature of the fuel contained therein. By means of tank insulation there is a reduced temperature rise during motor vehicle operation, which thus reduces the vapor pressure of the fuel and effectively re duces the evaporation losses from the fuel tank itself, through tank vent 42. Any conventional insulating maexternal vent '22 of4float bowl 13. Thus, there is communication between the vapor space of fuel tank lb and the vapor space of float bowl 1% which, during engine operation, will permit any vapors evaporating from fuel tank ltl'to passthrough tank vent 42' to float bowl l8 and thence through internal vent 24 to the throat, of the carburetor where these vapors are swept into the engine combustion chamberand burned. When the engine is stopped the same vapor path is provided which maintains float bowl'lfi and fuel tank lilat substantially the same pressure thus permitting easy draining of float bowl 18.

Return lines 30 and 34, undercertain design conditions,

' -i.e., when. said lines are not in continuous descent to fuel tank 10, and/ or do not have .suflicient size to relieve themselves of the gas or vapor which occupies this line space after the carburetor bowl has drained, can become system. As shown in FIGURE 1, vent 40 can be returned to'the air cleaner assembly to prevent the escape of volatile fuel vapors into the atmosphere during. engine.

operation, or it can beventeddirectly to the atmosphere if desired. The location of vent 40 in the fuel drain-back conduit is not critical. as long as it allows gas to escape from the .conduitfor effective draining. The outlet of any such vents should, preferably be located above the level of the fuel in float bowl 18.

An alternate method of operation of the apparatus shown in FIGURE 1 comprises starting the engine operation with drain valve 32 closed and carburetor float bowl 18 empty. Fuel is supplied to carburetor float bowl 18 as hreinbefore described, which fills and maintains an adequate fuel reservoir through the action of float valve 28. There is no flow of gasoline through the system shown by line 30, drain valve 32 and line 34 during engine operation. When the engine is stopped, fuel pump 14 stops and therefore no longer supplies fuel via line 16 to carburetor float bowl 18. Drain valve 32 is immediately opened upon engine stoppage and float bowl 18 is drained of its fuel content via line 30-, drain valve 32 and line .34 to fuel tank 10. Drain valve 32 is then closed prior to or coincident with resumption of engine operation. The opening and closing of drain valve 39, can

be effected by the engine intake manifold vacuum ifit is a vacuum actuated valve, or by the ignition, switch if a solenoid actuated valve, or manually if a conventional mechanical valve. The opening and closing of such valves is conventional and well-known in the art and hence need not be described in detail.

Referring now more particularly to FIGURE 2, the

apparatus here shown comprises a preferred embodiment of our fuel supply system. The volatile hydrocarbon fuel enters .fuel tank via inlet-conduit-124. The outer surface of fuel tank 100' is covered with about one inch of glasswool insulation 160. When fuel tank 100 is filled to the desired level, tank cap 126 seals inlet conduit 1.24. Tank cap 126 is 'a conventional pressure relief cap which maintains the fuel tank under a positive pressure between about '0 and about 2 p.s.i.g. The design of these soto develop within fuel tank 10! When pressures above about Zpsig. develop, a relief valve is opened to reduce the pressure to about 2 p.s.i.g. The fuel from tank 100 is supplied to carburetor float bowl 108 via line 102, fuel pump 104, fuel pressure regulator 105, and line 106. Fuel pump 104 in this preferred embodiment is an electrically operated pump which operates whenever the ignition is on and ceases operation, thus blocking the passage of fuel, when the ignition is off. Fuel pump 104, however, could be a conventional vacuum-operated fuel pump or a mechanical pump or the like. Conventional fuel pressure regulator 105 is an optional element of the fuel system whose use is dictated by the fuel pump used, the operating pressure of the fuel tank, and similar considerations. Normally these pressure regulators operate at between about 1 p.s.i.g. and about 5 p.s.i.g. fuel pressure to the carburetor. The fuel enters carburetor float bowl 108 from line 106 at a rate controlled by the pressure setting of fuel pressure regulator 105 and conventional float valve 116 which, as the fuel within float bowl 108 rises, restricts the entrance of line 106 into float bowl 108 and thus acts as a metering device to maintain a substantially constant level of fuel within car- .buretor float bowl 108.

The fuel drain-back system comprises a tubular line 118 opening from the bottom of float bowl 108, vacuum operated drain valve 120, and line 122 which opens into fuel tank 100. Fuel tank 100 is in communication with the atmosphere via line 128, vacuum operated vent valve 130 and conduit 132. The operation of valve 120 in the fuel drain-back system is controlled by a vacuum delay system comprising conduit 136, a small vacuum reservoir tank 138, conduit 140, check valve 142, and vacuum supply conduit 144.

The operation of the fuel supply system of this preferred embodiment starts with the initial filling through inlet conduit 124 of fuel tank 100 until the desired fuel level is obtained. Pressure cap 126 is then secured thus sealing the end of inlet conduit 124. Prior to starting the internal combustion engine of which this fuel supply system is a part, valve 130 is open and valve 120 is open. When the engine is started the vacuum actuated valves 120 and 130 close, and fuel is supplied to carburetor float bowl 108 via line 102, fuel pump 104, fuel pressure regulator 105, and line 106. Float bowl 108 is quickly filled to the operative level as controlled by float valve 116. During the period of engine operation, valve 120 and 130 remain closed. Keeping valve 130 closed prevents the escape of fuel vapors from the tank vent line 132 to the atmosphere, which, due to the slopping of the fuel Within the tank can be an appreciable source of hydrocarbon contaminant in the atmosphere. During engine operation any vapors which develop in float bowl 108 travel via internal vent112 to the other carburetor chambers and are thus swept into the combustion chambers of the engine and burned.

When the engine is shut off, the conventional vacuum manifold of the internal combustion engine returns to atmospheric pressure, thus dissipating the vacuum source which was holding valves 120 and 130 closed, and valve 130 opens immediately allowing tank-100 to come to atmospheric pressure. The opening of valve 120, however, is delayed by the action of vacuum reservoir tank 130. In a fuel system as herein described, it is necessary that tank 100 be near or at the same pressure as float bowl 108 when drain valve 120 is opened. Otherwise, there could be a reverse surge of fuel into float bowl 108 which would prevent proper drainage, and might even overflow into the engine compartment resulting in 6XCSSSiXB hydrocarbon loss to the atmosphere. When the engine vacuum manifold returns to atmospheric pressure, check valve 142 automatically closes thus allowing vacuum reservoir tank 138 to come gradually to atmospheric pressure by the entrance of air through orifice 146. The delay in opening valve 120 is thus a function of the size of orifice 146 and vacuum reservoir tank 138. A typical system has a time delay of about 15 seconds, and

comprises a vacuum reservoir volume of about 32 cubic inches and an orifice diameter of about 0.02 inch. Obviously, however, any other combination of orifice size and vacuum reservoir volume which would give the desired time delay could be used. Operative time delay periods of about 3 to 60 seconds are contemplated.

When the pressure in vacuum reservoir tank 138 approaches atmospheric, valve 120 opens and permits the fuel remaining in carburetor float bowl 108 to drain back to fuel tank 100 via line 118, opened drain valve 120, and line 122. Line 122 is supplied with an optional atmosphericvent 150 to air cleaner 114, which, as previously discussed with respect to FIGURE 1, allows the escape of trapped air and vapors in the drain-back conduit system thus allowing effective draining. When the engine is restarted, valves 120 and 130 close by action of the engine vacuum source, and the system repeats the first described mode of operation.

The fuel system as above described is not limited to the use of vacuum actuated valves. Valves 120 and 130 can be electrical solenoid valves with appropriate circuiting usually in conjunction with the ignition circuit. Thus, valves 120 and 130 would be in the open position when the ignition was off and in the closed position when the ignition was turned on. Instead of the vacuum delay system used to control valve 120, we may also use a conventional mechanical or electrical delay system. Valves 120 and 130 may also be mechanical valves operated manually. Although the fuel systems shown in FIG- URES 1 and 2 are illustrated With a single bowl carburetor, the method and apparatus of our invention have been successfully applied to an engine having a two-bowl carburetor, and any number of carburetors or bowls may be integrated into the system.

The air pollution abatement device of this invention is rugged by virtue of its simplicity, but should any maintenance or repair work be required, this can easily be accomplished since conventional parts, fittings, and equipment are used throughout.

While in the foregoing description, we have referred mainly to carburetor fuel induction systems, the invention in its broadest aspect is not limited thereto. Other fuel induction devices, such as pressure injectors may also draw from small intermediate fuel reservoirs located in the engine compartment. Our invention is hence applicable to any fuel supply systems involving a storage tank relatively remote from the engine, and a secondary vented reservoir located sufficiently near the engine to absorb heat therefrom.

It will be apparent from the foregoing that the apparatus of our invention includes a new and novel carburetion device comprising a housing enclosing an air-intake and fuel evaporation throat, an integrally attached fuel reservoir chamber, a fuel inlet opening into the reservoir chamber, at least one liquid fuel transfer port traversing the housing and communicating the throat with the reservoir chamber, means for maintaining a substantially constant liquid fuel level in the reservoir chamber against a supernatant vapor space, at least one balancing tube traversing the housing and connecting the supernatant vapor space in the fuel reservoir chamber with the throat, and a drain port opening from the bottom of the reservoir chamber.

Various other changes and modifications of this invention are apparent from the description of this invention and further modifications will be obvious to those skilled in the art. Such modifications and changes are intended to be included within the scope of this invention as defined by the following claims.

We claim:

1. In combination with an internal combustion engine, an improved liquid fuel delivery and conservation system adapted to minimize evaporative fuel losses, comprising in combination a remote fuel storage tank, a fuel induction device associated with said engine, an induction sysdelivery means;

tern fuel reservoir chamber located near said engine, said chamber having a supernatant vapor space and having at least one vent to the atmosphere from said supernatant vapor space, fuel delivery means for delivering fuel from said storage tank to said fuel reservoir chamber, means for transferring fuel from said reservoir chamber to said fuel induction device, and a fluid drain conduit opening from said fuel reservoir chamber and communicating with the interior of said storage tank, said drain conduit being adapted to return fuel to said storage tank, and to empty said reservoir chamber when. said fuel delivery means is inoperative.

2. A combination as defined in claim 1 wherein said fuel induction device is a carburetor, and said induction system fuel reservoir chamber is a float chamber provided with a float valve therein for controlling the rate of fuel inflow to maintain a constant liquid level therein.

3. A combination as defined in claim 2 wherein said supernatant, vapor space of said reservoir chamber is vented to the atmosphere through an internal vent of said carburetor, and contains no external vents.

4. A combination as defined in claim 1 including a vent communicating with the atmosphere from the vapor space in said fuel storage tank.

5. A combination as defined inclairn 4 wherein, the vent opening from said storage tank is a first vapor conduit leading into and communicating with the vapor space in said fuclreservoir chamber, saidstorage tank being vented to the atmosphere through said first vapor conduit x 6. [A combination asdefine'd -in cum, 1; muusin inpl regulatingmeans' in said drain 'conduitpadapte'dfto limit the flow rate from said fuel reservoir chamberto a value substantially lower than the delivery capacity of said fuel "7. A' combiriation as defined in claim l includin valve in said drain conduit, and control means for closing said valve during engine operation, and for opening the point in said drain conduit and phere. I

9. In combination opening to the atmos with an internal combustion engine,

an improved liquid fuel delivery andconservation -sysfc rbureito p r p, a

5 A ci'buretor or use ininternal com ustionengines] comprising au horis ng enclosing an air-intake and fuel 1 evaporation threat, a. fuel reservoir chamber; a fuel inter I Y openinginto "fuel transfer por traversing said he ingand municating the interior of said reservoir tank with a' variable pressure zone, the pressure in said variable pressure zone being supplied by operation of said internal combustion'engine and differing from the pressure in said substantially constant pressure zone by an amount sufficient to operate said pressure operated device in one direction; and a check valve in said second conduit adapted to close whenthe pressure of said variable pressure zone approaches the pressure of said constant pressure zone, said orifice having a flow capacity substantially less than the flow capacity of said second conduit and havinga flow capacity whiohrequires a substantial period of time to equalize the. pressure between said constant pressure Zone and said reservoir tank when said check valve closes.

11. An apparatus as defined in claim10 wherein said period of time required to equalize the pressure is between about 3 and about seconds.

12. A combination as defined in claim 9 including a fuel inletport to said storage tank, a removable cap closing said inlet port, and wherein said pressure relief valve andsaid check valve are positioned in said removable cap. I i v 13. Acombination as defined in claim 9 wherein said supernatant vapor space of said, reservoir chamber is ndfcodtains rid external vent ea tone catingsaid throat with said reservoir chamber, means for maintaining a substantially constant liquidfuel level in said reservoir chamber against a supernatant vapor space, at least one balancing tube traversing said housing and.

communicating said vapor spacewith said throat, and a drain port openingfrom the bottom of said reservoir chamber.

tern adapted to minimize evaporative fuel losses, cornprising in combination a fuel storage tank, a pressure relief valve in the upper portion of said'storage tank adapted to maintain a small maximum positive pressure therein, a check valve in the upper portion of said storage tank adapted to maintain at least atmospheric pressure therein, anindependently operable valve in the upper portion of said storage tank, means for maintaining said independently operable valve closed when said engine is in operation and for opening the same 'tothe atmosphere substantially simultaneously with each cessation of engine operation, a carburetor having a fuel reservoir chamber with a supernatant vapor space and with at least one vent to the atmosphere from said supernatant vapor space, means for delivering fuel from said storage tank to said fuel reservoir chamber, a fluid drain conduit opening from said fuel reservoir chamberand communicating with the interior of said storage tank, said drain conduit being adapted to return fuel tosaid storage tank, and to empty said reservoir chamber, a throttle valve in said drain conduit, and control means for maintaining saidthrottle A methodiof reducing fuel evaporation frornqthe fuel supply system of an, internal; combustion engine having a carburetor with r a fuel'containing reservoir chamber, saidichamber. havinga supernatantvapor space. i

in vapor communication with the, atmosphere, which method comprises: opening a drain port in the bottom of said chamber andemptying said chamber by draining, retained fuel to the fuel storage tank immediately after stopping said engine, saiddrain port being closed while the engine is in operation; and closing said drain port after i ber located near said engine, said fuel reservoir chamber. having a supernatant vapor spaceoand having at least one,

retained in said reservoir chamber after stopping said engine 17. Apparatus according to claim 16 in which. said cooling 'means comprises a cool fuel-containing storage tank located at a position more remote from said engine than said reservoir chamber, andftransfer means for transfernng fuel from said reservoir chamber to said storage tank when said engine is stopped.

18. In a system for delivering a volatile fuel to an internal combustion engine, wherein a fuel reservoir chamof said. l

communh her is located adjacent to the engine, said fuel reservoir chamber having at least one vent communicating its vapor space with the atmosphere, and said reservoir chamber is provided with fuel inlet, fuel outlet, and level control means for maintaining a substantially constant level of liquid fuel in said reservoir during operation of said engine, the improvement which comprises transfer means for transferring said fuel from said reservoir to a second chamber when said engine is not in operation.

19. An apparatus for use with an internal combustion engine which comprises in combination, a liquid fuel storage tank, a fuel induction device associated with said engine, an induction system fuel reservoir chamber vented to the atmosphere through an internal vent of said fuel induction device, and a conduit communicating the vapor space of said storage tank with an air intake channel of said internal combustion engine, and transfer means for transferring fuel from said reservoir chamber upon cessation of engine operation.

20. An apparatus for use with an internal combustion engine which comprises in combination, a liquid fuel storage tank, a fuel induction device associated with said engine, an induction system fuel reservoir chamber, a first conduit communicating the vapor space of said storage tank with the supernatant vapor space of said fuel reservoir chamber, and an internal vent communicating said supernatant vapor space with the air intake channel of said fuel induction device.

21. An operational delay apparatus for controlling a pressure operated device which reciprocally operates by changing pressure, which comprises: a substantially constant pressure source; a variable pressure source which is capable of attaining the same pressure as said constant pressure source as well as a pressure which differs from said constant pressure source by an amount sufiicient to operate said pressure operated device; a reservoir tank communicating said pressure operated device with said variable pressure source; an orifice in said reservoir tank communicating the interior of said tank with said constant pressure source, said orifice having a flow capacity substantially less than the flow capacity between said reservoir tank and said variable pressure source; and a check valve located between said variable pressure source and said reservoir tank, said check valve being adapted to close only when the pressure of said variable pressure source approaches the pressure of said constant pressure source. I

22. An apparatus as defined in claim 21 wherein said substantially constant pressure source is at a higher pressure than said variable pressure source.

23. An apparatus as defined in claim 21 wherein said substantially constant pressure source is at atmospheric pressure, and wherein said variable pressure source is at subatmospheric pressure.

24. A method of reducing fuel evaporation from the fuel supply system of an internal combustion engine having a carburetor with a fuel-containing reservoir chamber whose supernatant vapor space is in vapor communication with the atmosphere, which method comprises: transferring all of the retained fuel from said fuel-containing chamber to a remotely located cool fuel-containing storage tank within a short period of time after stopping said engine.

25. A method as defined in claim 24 wherein said period of time is not greater than about 4 minutes.

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